Microstructural Evolution and Properties of ZrB2-Reinforced AA6111 Aluminum Matrix Composites Subjected to Double-Sided Friction Stir Processing

Single-sided friction stir processing (S-FSP), owing to its intrinsic structural characteristics, including the advancing side and the retreating side and the nonuniformity of attributes, restricts the enhancement of the strength of aluminum composite materials. Herein, the preparation of AA6111/ZrB₂ aluminum matrix composites, 4 mm in thickness, via an in situ autogenous casting process is presented. The composites undergo double-sided FSP (D-FSP) with varying parameters, utilizing an orthogonal test method. In these findings, it is indicated that the mean grain size of the nugget zone (NZ) post D-FSP is reduced from 5.56 μm in S-FSP to 4.65 μm, the percentage of low-angle grain boundaries diminishes from 31.4% to 26.9%, and the recrystallized structure escalates from 49.7% to 65.2%. At a rotational speed of 1000 r min⁻¹ and a processing speed of 40 mm min⁻¹, the average hardness of the NZ of D-FSP is augmented by 6.3% relative to S-FSP; the ultimate tensile strength and elongation of the material are enhanced by 1.6% and 31.7%, respectively, compared to S-FSP, while the product of strength and elongation is increased by 33.2%.